The present invention relates to sunken lawn sprinklers which are automatically projected or advanced to a position above the surrounding ground level when water pressure is applied to the sprinkler.
Many parks and schools, athletic fields, golf courses, and residences are installing automatic irrigation systems to provide adequate moisture for landscaping and to maintain vast acres of lawn inter to a high degree of perfection. In such applications the pop-up type of sprinkler heads have been found most desirable to facilitate ground maintenance. Further, by using pop-up sprinkler heads which retract out of sight when not in use, the hazards associated with permanently elevated obstruction are eliminated. Such hazards include accidents incurred by tripping or falling over the sprinkler, striking the sprinkler with a lawnmower or automobile, and theft of a permanently elevated sprinkler head.
Many forms of projectable sprinklers have been proposed both commercially and in the patent literature. U.S. Pat. Nos. 3,758,038; 3,104,822; 2,611,644; and 2,013,849 disclose various types of pressure operated pop-up sprinklers. By the term "pressure operated" is meant that the lawn sprinklers are projected up by the pressure of the water supplied to the sprinklers. Another method of raising or projecting a sprinkler is disclosed in U.S. Pat. Nos. 3,921,911 and 3,709,435 wherein the projectable lawn sprinklers float upward from the ground.
One difficulty encountered in making a commerically successful pressure operated lawn sprinkler has been the complexity and number of parts required. Some sprinklers are costly to manufacture, difficult to assemble, repair and service, and are unreliable in operation. Furthermore, pressure operated pop-up sprinklers have suffered from the inability to seal well. Poor sealing causes an unnecessary large drop in pressure with the result that fewer projectable sprinklers than permanently raised sprinklers could be used on a supply line of given hydraulic capacity.
A further problem encountered in prior art, projectable lawn sprinklers was that to prevent the stand pipe projected from the ground from rocking, it was necessary to have the relatively movable parts fit one another quite closely and to have lengthy bearing surfaces, i.e., lands. However, when the parts fit closely, natural friction develops and foreign matter tends to stick between the parts. This sometimes jams the stand pipe, and at other times scores the parts so as to permit leakage to develop. Furthermore, the use of long lands requires additional force to raise the stand pipe, and it is therefore more vulnerable to jamming.
An additional problem encountered in pressure operated pop-up sprinklers is the need to control the rate at which the sprinkler rises. If the sprinkler head rises rapidly when water pressure is applied to the sprinkler, the projectable casing can strike the stationary casing with great impact which could cause possible damage to the sprinkler.
Additional disadvantages of some pressure operated projectable lawn sprinklers is that they do not tend to assume and maintain the predetermined substantially vertical position each time they are erected, that they do not erect to great heights because clearances and friction are multiplied when the movement of the stand pipe becomes appreciable, and that grass can grow over the top of the projectable lawn sprinkler and prevent the sprinkler from rising.